Filter media and elements

ABSTRACT

Fibrous filter medium that includes a melt-blown filter layer comprising melt-blown fibers and a high-efficiency glass-containing filter layer comprising glass fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/776,447, filed Sep. 14, 2015, which is a U S. National StageApplication of International Application No. PCT/US2014/020698, filed onMar. 5, 2014, which claims the benefit of U.S. Provisional ApplicationSer. No. 61/835,881, filed Jun. 17, 2013, and U.S. ProvisionalApplication Ser. No. 61/788,876, filed Mar. 15, 2013, each of which areincorporated herein by reference in their entireties.

BACKGROUND

Fluid streams, particularly air and gas streams, often carry particulatematerial therein. The removal of some or all of the particulate materialfrom the fluid stream is needed. For example, air intake streams to thecabins of motorized vehicles, air in computer disk drives, HVAC air,clean room ventilation air, air to engines for vehicles or powergeneration equipment, gas streams directed to gas turbines, and airstreams to various combustion furnaces, often include particulatematerial therein in the case of cabin air filters it is desirable toremove the particulate matter for comfort of the passengers and/or foraesthetics. With respect to air and gas intake streams to engines, gasturbines and combustion furnaces, it is desirable to remove theparticulate material because particulate can cause substantial damage tothe internal workings of the various mechanisms involved. In otherinstances, production gases or off-gases from industrial processes orengines may contain particulate material therein. Before such gases aredischarged to the atmosphere, it is typically desirable to obtain asubstantial removal of particulate material from those streams.

Higher and higher efficiency filters are needed to get cleaner air orgas streams. Low pressure is desired to have less restriction to airflow caused by high efficiency filters. Also, longer life is desired toreduce the maintenance and filter costs, which is often a challenge inhigh efficiency filters. Thus, there continues to be a need for highperformance filters, i.e., high efficiency, low pressure-drop, long-lifefilters.

In certain environments where air filtration is required in highly humidenvironments, such as off-shore and coastal environments, conventionalfilter media are unsuitable. For example, such filter media may not bewatertight. Thus, there continues to be a need for new filter media insuch applications.

Furthermore, although the filter media and filters of the presentdisclosure may be used in a variety of applications, they areparticularly suitable for use with gas turbine filter systems. Gasturbine systems are useful in generating electricity, and they utilizeair for combustion purposes. Due to the precision moving parts in thesetypes of systems, the combustion air needs to be clean. To ensure cleanair for combustion, air filters have been used to clean the air takeninto the gas turbine system. New requirements from the Power Generationindustry require even cleaner air entering the turbine blades thanpreviously required. Conventional filter media do not have sufficientperformance characteristics (e.g., sufficiently high efficiencyfiltration while maintaining a low pressure drop) to prevent compressorblade fouling, which reduces the overall efficiency of the turbine.

SUMMARY

The present disclosure provides filter media and filter elements,particularly for air filtration applications.

In one embodiment, there is provided a filter medium that includes: amelt-blown filter layer including melt-blown fibers; and aglass-containing filter layer including glass fibers. During use, thelayers are positioned relative to each other such that the melt-blownfilter layer is positioned as the first layer encountered by the airstream being filtered. That is, in the filter media and filter elementsof the present disclosure, the melt-blown filter layer is the mostupstream layer.

In one embodiment, there is provided an air filter medium that includes:a melt-blown filter layer including melt-blown fibers; and ahigh-efficiency glass-containing filter layer including glass fibers andmulti-component binder fibers; and an optional support layer; whereinthe layers are configured and arranged for placement in an air stream.

In certain embodiments, the melt-blown fibers have an average diameterof greater than 1.5 microns, and in certain embodiments at least 2microns. In certain embodiments, the melt-blown layer has acompressibility of greater than 40% at a pressure of 17.6 psi (i.e.,1.24 kg/cm²).

In certain embodiments, the glass fibers have an average diameter ofless than 2 microns, and in certain embodiments less than 1 micron. Incertain embodiments, the glass-containing filter layer includesmulti-component (e.g., bicomponent) binder fibers.

In certain embodiments, the filter medium includes a support layer. Asupport layer is typically necessary when forming a pleated filterelement. In certain embodiments, the support layer includes fibershaving an average diameter of at least 5 microns, and in certainembodiments at least 10 microns. In certain embodiments, the supportlayer has a stiffness of 100 grams or more, and in certain embodiments,300 grams or more.

In one embodiment of the present disclosure, there is provided a filtermedium that includes: a melt-blown filter layer including melt-blownfibers having an average diameter of greater than 1.5 microns; whereinthe melt-blown filter layer has a compressibility of greater than 40% ata pressure of 1.24 kg/cm²; a high-efficiency glass-containing filterlayer including glass fibers and multi-component binder fibers; and aspunbond support layer.

In another embodiment of the present disclosure, there is provided anair filter element that includes a housing and a fibrous filter mediumas described herein.

In another embodiment of the present disclosure, there is provided amethod of filtering air, the method including directing the air througha filter medium or filter element as described herein.

In one embodiment, there is provided a method that involves directingthe air through a filter medium that includes: a melt-blown filter layerincluding melt-blown fibers; a high-efficiency glass-containing filterlayer including glass fibers and multi-component binder fibers; and asupport layer; wherein the melt-blown filter layer is the most upstreamlayer.

Herein, “high-efficiency” means a filter layer, media, or element of thepresent disclosure is able to remove at least 70% (by number) of0.4-micron size DEHS particles at its rated velocity. For example, afiltration efficiency of at least 70% of the most penetrating particlesize (MPPS) particulates (which may be smaller than 0.4 microns) isconsidered “high efficiency.” In certain embodiments herein,high-efficiency means removing at least 85%, at least 95%, at least99.5%, at least 99.95%, or at least 99.995%, of such particles, at itsrated velocity. In this context, “at its rated velocity” means thevelocity of the air going through the media when the filter element isbeing operated at its rated flow rate (CFM) in its intended application,as determined by the media flow rate divided by square footage of mediain the filter element.

The term “melt-blown fibers” refers to fibers formed by extruding amolten thermoplastic material through a plurality of fine, usuallycircular, die capillaries as molten threads or filaments into converginghigh velocity gas (e.g., air) streams which attenuate the filaments ofmolten thermoplastic material to reduce their diameter, which may be tomicrofiber diameter. Thereafter, the melt-blown fibers are carried bythe high velocity gas stream and are deposited on a collecting surfaceto form a web of randomly dispersed melt-blown fibers. Typically,melt-blown fibers are microfibers which may be continuous ordiscontinuous, are generally equal to or smaller than 20 microns (andoften 10 microns) in diameter, and are generally self bonding whendeposited onto a collecting surface. Melt-blown fibers used in thepresent invention are preferably substantially continuous in length.

The term “spunbond fibers” refers to small diameter fibers formed byextruding molten thermoplastic material as filaments from a plurality offine capillaries of a spinnerette having a circular or otherconfiguration, with the diameter of the extruded filaments then beingrapidly reduced. Spunbond fibers are quenched and generally not tackywhen they are deposited onto a collecting surface. Spunbond fibers aregenerally continuous and often have average diameters larger than 7microns, and often, 10 to 30 microns.

The term “multi-component fibers” refers to fibers formed from at leasttwo polymers extruded separately but spun together to form one fiber. Asa particular example of a multi-component fiber, a “bicomponent fiber”includes two polymers arranged in substantially constantly positioneddistinct zones across the cross-section of the bicomponent fiber andextend continuously along the length of the bicomponent fiber. Theconfiguration of such a bicomponent fiber may be, for example, asheath/core configuration wherein one polymer is surrounded by anotheror may be a side-by-side configuration or an “islands-in-the-sea”configuration. For two component fibers, the polymers may be present inratios of 75/25, 50/50, 25/75 or any other desired ratios. Conventionaladditives, such as pigments and surfactants, may be incorporated intoone or both polymer streams, or applied to the filament surfaces.

The term “polymer” includes, but is not limited to, homopolymers,copolymers, such as for example, block, graft, random, and alternatingcopolymers, terpolymers, etc., and blends and modifications thereof.Furthermore, unless otherwise specifically limited, the term “polymer”shall include all possible geometrical configurations of the material.These configurations include, but are not limited to, isotactic,syndiotactic, and atactic symmetries.

The term “electrostatic charging” refers to a process that places acharge in and/or on a dielectric material such as a polyolefin. Thecharge typically includes layers of positive or negative charges trappedat or near the surface of the polymer, or charge clouds stored in thebulk of the polymer. The charge may also include polarization chargeswhich are frozen in alignment of the dipoles of the molecules. Methodsof subjecting a material to an electric charge are well known by thoseskilled in the art. These methods include, for example, thermal,liquid-contact, electron beam, plasma, and corona discharge methods.

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims. Suchterms will be understood to imply the inclusion of a stated step orelement or group of steps or elements but not the exclusion of any otherstep or element or group of steps or elements. By “consisting of” ismeant including, and limited to, whatever follows the phrase “consistingof” Thus, the phrase “consisting of” indicates that the listed elementsare required or mandatory, and that no other elements may be present. By“consisting essentially of” is meant including any elements listed afterthe phrase, and limited to other elements that do not interfere with orcontribute to the activity or action specified in the disclosure for thelisted elements. Thus, the phrase “consisting essentially of” indicatesthat the listed elements are required or mandatory, but that otherelements are optional and may or may not be present depending uponwhether or not they materially affect the activity or action of thelisted elements.

The words “preferred” and “preferably” refer to embodiments of thedisclosure that may afford certain benefits, under certaincircumstances. However, other embodiments may also be preferred, underthe same or other circumstances. Furthermore, the recitation of one ormore preferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the disclosure.

In this application, terms such as “a,” “an,” and “the” are not intendedto refer to only a singular entity, but include the general class ofwhich a specific example may be used for illustration. The terms “a,”“an,” and “the” are used interchangeably with the term “at least one.”

The phrases “at least one of” and “comprises at least one of” followedby a list refers to any one of the items in the list and any combinationof two or more items in the list.

As used herein, the term “or” is generally employed in its usual senseincluding “and/or” unless the content clearly dictates otherwise. Theterm “and/or” means one or all of the listed elements or a combinationof any two or more of the listed elements.

Also herein, all numbers are assumed to be modified by the term “about”and preferably by the term “exactly.” As used herein in connection witha measured quantity, the term “about” refers to that variation in themeasured quantity as would be expected by the skilled artisan making themeasurement and exercising a level of care commensurate with theobjective of the measurement and the precision of the measuringequipment used.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range as well as the endpoints (e.g., 1to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). Herein, “up to” anumber (e.g., up to 50) includes the number (e.g., 50).

The above summary of the present disclosure is not intended to describeeach disclosed embodiment or every implementation of the presentdisclosure. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through lists of examples, which examples can beused in various combinations. In each instance, the recited list servesonly as a representative group and should not be interpreted as anexclusive list.

DRAWINGS

The disclosure may be more completely understood in connection with thefollowing drawings.

FIG. 1 is a cross sectional view of an embodiment of a composite filtermedia of the present disclosure.

FIG. 2 is a cross sectional view of another embodiment of a compositefilter media of the present disclosure.

FIG. 3 is a cross sectional vie of still another embodiment of acomposite filter media of the present disclosure.

FIG. 4 is a perspective view of one embodiment of a filter elementusable in an air intake system.

FIG. 5 is a perspective view of another embodiment of another elementwith a filter medium of the disclosure.

FIG. 6 is a top plan view of another filter element of the disclosureusable in an air intake.

FIG. 7 is a front elevational view of the element of FIG. 6,

FIG. 8 is a right side elevational view of the filter element of FIG. 7.

FIGS. 9-13 are schematic, cross-sectional views of further embodimentsof filter elements usable in an air intake for a gas turbine system.

FIG. 14 is a perspective view of another embodiment of element usable inan air intake for a gas turbine system.

FIG. 15 is a schematic, side view of one embodiment of a filtrationsystem for a gas turbine air intake, constructed in accordance withprinciples of this disclosure.

FIG. 16 is a top view of the system of FIG. 15.

FIG. 17 is a perspective view of one embodiment of a watertight filterthat is usable in the filtration system of FIGS. 15 and 16.

FIG. 18 is a schematic, cross sectional view of the filter media used inthe watertight filter element of FIG. 17.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure provides a filter medium that includes amelt-blown filter layer and a high-efficiency glass-containing filterlayer, and an optional support layer. Such filter media can be used in avariety of filtration methods, but primarily in air filtrationtechniques. In particular uses, the filter media of the presentdisclosure are preferably used in gas turbine filter systems.

The relative orientation of the melt-blown filter layer, high-efficiencyglass-containing filter layer, and optional support layer can varydepending on the use of the composite medium. Typically, the orientationcan vary as long as the melt-blown filter layer is positioned as thefirst layer encountered by the air stream during use (i.e., the mostupstream layer). In certain embodiments, a support layer is positionedbetween the melt-blown layer and the glass-containing layer. In certainembodiments, the glass-containing layer is positioned between themelt-blown layer and the support layer.

Each filter layer and support layer can be a composite of multiplelayers. For example, the melt-blown filter layer can be a composite oftwo or more different layers of melt-blown fibers, either differing incomposition and/or fiber diameter.

In certain embodiments, a composite filter media includes two or moremelt-blown fiber layers. In certain embodiments, a composite filtermedia includes two or more glass-containing fiber layers. In certainembodiments, a composite filter media includes two or more supportlayers. These layers can be arranged in a variety of orders as long asone of the melt-blown filter layers is the most upstream layer.

As shown in FIG. 1, which shows an exemplary composite filter medium 10of the present disclosure, there are at least two filter layers, i.e.,layers that perform filtration: a melt-blown filter layer 18 and aglass-containing filter layer 20. As shown in this exemplary embodiment,the melt-blown filter layer 18 is positioned upstream of theglass-containing filter layer 20 relative to the direction of air flow(indicated by an arrow). That is, the melt-blown filter layer 18 is thefirst layer encountered by the air stream during use.

In certain embodiments, the composite filter media also include asupport layer (i.e., substrate). This allows for the filter media to becorrugatable and/or pleatable. The support layer may be positionedeither upstream or downstream of the glass-containing filter layerrelative to the air flow through the filter. Shown in FIG. 2 is a filtermedium (i.e., filtration medium) 10 comprising a support layer 22disposed on the downstream side of glass-containing filter layer 20. InFIG. 3 support layer 22 is disposed on the upstream side ofglass-containing filter layer 20 between melt-blown filter layer 18 andglass-containing filter layer 20.

The thicknesses of each of the filter and support layers may be the sameor different. Thus, the relative sizes shown in FIGS. 1-3 are notlimiting. However, it is noted that thickness has an effect onfiltration properties. The overall thickness of the media is desirablyminimized without significantly affecting the other media properties,such as dust loading capacity, efficiency, and permeability. This allowsfor more pleats in an element, for example, preferably such that afilter element includes a maximum amount of media without adverselyaffecting the filter element properties and performance (e.g.,efficiency, pressure drop, or dust loading capacity).

In certain embodiments, a scrim can be used to create a layer downstreamfrom the glass-containing layer to capture any glass fibers releasedfrom the glass-containing layer for preventing or reducing introductionof glass fibers into the filtered air. The filtration layer of fiberglass medium has two faces. Useful materials for the scrim (i.e.,filtration layer for the glass fibers) typically have a highpermeability (i.e., “perm”) (e.g., greater than 16001/m²/s) and are thin(e.g., less than 0.005 inch) so there is a minimal effect on the flatsheet or filter element performance. Examples of such scrim materialsinclude those available under the tradenames FINON C303NW and FINONC3019 NW from Midwest Filtration in Cincinatti, Ohio. Others aredescribed, for example, in U.S. Pat. Pub. 2009/0120868.

The layers are typically laminated together so the melt-blown layer isthe furthest upstream, the spunbond is downstream from the melt-blownlayer, the wet-laid glass-containing layer is just downstream of thespunbond layer, and the scrim (if present) is on the most downstreamside. Alternatively, the wet-laid glass-containing layer is positionedbetween the melt-blown layer and the spunbond layer.

Typically, in a filter medium of the present disclosure, the filterlayers, and preferably, the filter and support layers are adheredtogether with an adhesive, through thermal bonding or ultrasonicbonding, through the use of binder fibers, or using a combination ofsuch techniques. Preferred methods include the use of an adhesive,binder fibers, or a combination thereof. A particularly preferred methodis through the use of an adhesive (pressure sensitive adhesives, hotmelt adhesives) applied in a variety of techniques, including, forexample, powder coating, spray coating, or the use of a pre-formedadhesive web. Typically, the adhesive is in a continuous layer, or itcan be patterned if so desired as long as the filter medium does notdelaminate during processing or use. Exemplary adhesives include hotmelt adhesives such as polyesters, polyamides, acrylates, orcombinations thereof (blends or copolymers).

If an adhesive is used, the amount of adhesive can be readily determinedby one of skill in the art. A desired level is one that providessuitable bonding between the layers without adversely impacting the airflow through the media. For example, the reduction of the Frazierpermeability of a composite filter medium is preferably less than 20%,or more preferably less than 10%, of the inverse of the sum of theinverse of each layer's permeability (i.e.,(1/A_(perm)+1/B_(perm)+1/C_(perm))⁻¹). This is also applicable for anyother lamination methods.

In order to increase rigidity and provide better flow channel in anelement, a filter medium can be corrugated. Thus, preferred filter mediaof the present disclosure should have the characteristics to survive atypical hot corrugation process without media damage (which oftendeteriorate the media performance). Preferred filter media should alsohave the ability to maintain the depth of the corrugations (e.g.,0.020-0.035 inch, 0.5 mm to 0.9 mm) through further processing, storage,transportation, and use. Typically, there should not be more than 20%reduction in corrugation depth, or not more than 30% reduction incorrugation depth, or not more than 50% reduction in corrugation depth,after the corrugations are formed (as a result of handling duringfurther processing, storage, transportation, and use). These propertiesare typically related to media composition, as well as material strengthand stiffness.

With or without the corrugation, a filter medium can be folded intomultiple folds or pleats and then installed in a filter housing orframe. Pleating of a flat sheet or corrugated sheet can be carried outusing any number of pleating techniques, including but not limited to,rotary pleating, blade pleating, and the like. The corrugated media mayhave any one of several pleat supporting mechanisms applied to thepleated media as described in U.S. Pat. No. 5,306,321. For example,corrugated aluminum separators, hot melt beads, and indentations (oftenreferred to as PLEATLOC pleated media) can be used.

In certain embodiments, a fold is imprinted into the filter media in aspacer form so bonding of the folds is prevented in an effective way,even in cases if the media is moist or overloaded. These dents on thepleat tips that are vertical to the corrugation channel direction onboth sides of the media, keep pleats separated, and provide better flowchannels for air to flow through the pleat pack in an element. If in aconical or cylindrical type element, such as that shown in FIGS. 9-14,dents on the outside can be deeper and wider than those on the inside tokeep even separation in pleats.

For a noncorrugated media, other pleat separation methods can be used onany of the media described herein, such as those involving the additionof a hot-melt adhesive bead between the pleats, or the use of combseparators. The pleated material can be formed into a cylinder or “tube”and then bonded together, such as through the use of an adhesive (e.g.,a urethane-based, hot-melt adhesive, etc.) or ultrasonic welding, forexample.

The filter media of the present disclosure can be incorporated into avariety of standard filter element forms, such as the WAVE filterelement depicted in U.S. Design Pat. No. 677370 or described inInternational Pub. No. WO 2010/151580.

In certain embodiments, filter layers, composite filter media (flat orcorrugated), and filter elements of the present disclosure are referredto as “high efficiency.” In certain embodiments, a filter layer,composite filter medium, or filter element of the present disclosuredisplays a filtration efficiency of at least 70% with 0.4-micron sizeDEHS (di-ethyl-hexyl-sebacat) particles at its rated velocity.Preferably, the filtration efficiency is at least 85%, or at least 95%,or at least 99.5%, or at least 99.95%, or at least 99.995% of the mostpenetrating particle size particles (MPPS) at its rated velocity (i.e.,rated flow rate in cubic feet per minute divided by square footage ofmedia in the element).

In certain embodiments, a filter layer, composite filter medium and/orfilter element of the present disclosure is watertight. As used herein,a “watertight” filter medium or element means that the medium or elementwill prevent bulk water or water droplets from passing through thefilter medium and/or the filter element for several hours under heavywater spray conditions while being operated at the filter's rated flowrate. The watertight characteristics of the filter element can bemeasured using the Water Spray Test described in the Examples. Thewatertight characteristics of the media can be measured by thehydrostatic head test described in the Examples. In certain embodiments,a filter medium and/or element of the present disclosure displays ahydrostatic head of at least 10 inches (25.4 cm) of water, or at least15 inches (38.1 cm) of water, or at least 20 inches (50.8 cm) of water.

In certain embodiments, a filter layer and/or composite filter medium ofthe present disclosure has good depth loading characteristics.

In certain embodiments, a filter layer, composite filter medium (whichmay or may not be corrugated) and/or filter element of the presentdisclosure displays a salt loading capacity of at least 10 grams persquare meter (g/m²) at a terminal pressure drop of 4 inches water column(i.e., 1000 Pa). Typically, the higher salt loading capacity the better,as this is an indicator of life of the product.

In certain embodiments, a filter layer, composite filter medium (whichmay or may not be corrugated) and/or filter element of the presentdisclosure displays a dust loading capacity of at least 30 grams persquare foot (g/ft²) of ASHRAE dust (per ASHRAE 52.2-2007 or EN779:2012)when loaded to 4 inches of water (i.e., 1000 Pa) dP (pressure drop) instatic mode (as opposed to pulsing mode). Typically, the higher dustloading capacity the better, as this is an indicator of life of theproduct.

In certain embodiments, a composite filter medium (which may or may notbe corrugated) and/or filter element (which is typically corrugated andpleated) of the present disclosure displays an efficiency of at least F9per EN779:2012.

In certain embodiments, composite filter medium (which may or may not becorrugated) and/or a filter element (which is typically corrugated andpleated) of the present disclosure displays an efficiency of at leastE10, or at least E11, or at least E12 per EN1822:2009.

In certain embodiments, a filter layer and/or composite filter mediumhas a relatively low solidity. As used herein, solidity is the solidfiber volume divided by the total volume of the filter medium at issue,usually expressed as a percentage, or put another way, the volumefraction of media occupied by the fibers as a ratio of the fibers volumeper unit mass divided by the media's volume per unit mass. A suitabletest for determining solidity is, for example, as follows. Solidity canbe measured by performing a solvent extraction of resin from the mediumto determine resin density. The percent resin, density of media(calculated from basis weight and thickness), density of the resin, anddensity of the fibers is used. TGA can be used to determine relativequantities of the materials in the medium. Literature values fordensities of fiber components can also be used, and the value analyzedusing the following equation:

${{Solidity}\%} = \frac{100}{\frac{1}{\frac{\rho_{media}}{{\frac{{Binder}\%}{100}/\rho_{binder}} + {\frac{{100} - {{Binder}\%}}{100}/\rho_{fiber}}}}}$

Typically, a solidity of less than 20 percent (%) at a pressure of 1.5psi (i.e., 0.1 kg/cm²), or often less than 15%, is desirable.

In certain embodiments, a filter layer and/or composite filter mediumhas a relatively high compressibility. Compressibility can be measuredby comparing two thickness measurements using a dial comparator, withcompressibility being the relative loss of thickness from a 2 ounce(56.7 g) to a 9 ounce (255.2 g) total weight (0.125 psi-0.563 psi or 8.6millibars-38.8 millibars), as described in U.S. Pat. No. 8,460,424.Another suitable test for determining compressibility is described inInternational Publication No. WO 2013/025445. Typically, acompressibility of greater than 40 percent at a pressure of 17.6 poundsper square inch (psi) (i.e., 1.24 kg/cm²) is desirable.

In certain embodiments, a filter layer and/or composite filter medium ofthe present disclosure demonstrates high strength and high flexibility.This can be demonstrated by a relatively low loss in tensile strengthafter a layer and/or a composite medium has been folded or corrugated.Less than 20% loss of tensile strength after folding or corrugation of afilter layer or filter medium is desirable.

In a preferred embodiment, a filter medium of the present disclosure isused in a gas turbine air-intake filtration system. Accordingly, thecomposite filter media is mounted into a frame so as to create anair-tight fit between the filter media and the frame, wherein the filtermedia is positioned such that at least one melt-blown filter layer isdisposed on an upstream side of the filter medium relative to adirection of air flow through the filter.

Melt-Blown Filter Layer

Typically, melt-blowing is a nonwoven web forming process that extrudesand draws molten polymer resins with heated, high velocity air to formfine filaments. The filaments are cooled and collected as a web onto amoving screen. The process is similar to the spun-bond process, butmelt-blown fibers are typically much finer. Typically, the melt-blownfibers have an average diameter of no greater than 20 microns. Incertain embodiments, the melt-blown filter layer includes melt-blownfibers having an average diameter of greater than 1.5 microns. Incertain embodiments, the melt-blown filter layer includes melt-blownfibers having an average diameter of at least 2 microns. In certainembodiments, the melt-blown fibers have an average diameter of 2-3microns.

In certain embodiments, the melt-blown filter layer has a relativelyhigh compressibility. In certain embodiments, a melt-blown filter layerof a filter medium of the present disclosure has a compressibility ofgreater than 40 percent at a pressure of 17.6 pounds per square inch(psi) (i.e., 1.24 kg/cm²). In certain embodiments, a melt-blown filterlayer of a filter medium of the present disclosure has a compressibilityof up to 90 percent at a pressure of 17.6 pounds per square inch (psi)(i.e., 1.24 kg/cm²).

In certain embodiments, scaffold fibers as described in InternationalPublication No. WO 2013/025445 can be included in the melt-blown filterlayer if desired for enhancing performance. However, media with highlevels of compressibility have little or no scaffold fibers used asdescribed in International Publication No. WO 2013/025445 in themelt-blown filter layer. The scaffold fibers provide support for themedia fiber, and add improved handling, greater tensile strength, andresults in lower compressibility to the media.

In certain embodiments, the melt-blown filter layer is electrostaticallycharged. This is typically done to enhance particle capture efficiency.The charge may be induced triboelectrically or by applying a highvoltage charge. The former is a result of rubbing the fibers against agrounded, conductive surface, or rubbing two different fibers againsteach other (one is more electropositive and the other is moreelectronegative). Alternatively, electrostatic charging can be carriedout using, for example, corona discharge or plasma discharge methods.Such methods are known to one of skill in the art. The extent ofelectrostatic charging done herein is what is conventionally done withmelt-blown fibers.

In certain embodiments, the melt-blown filter layer includes acontinuously gradient structure of larger fibers and more open structureat a first major surface and smaller fibers and less open structure at asecond major surface. In certain embodiments of this construction, thesecond major surface of the melt-blown filter layer is adjacent thesupport layer and the first major surface is positioned as the mostupstream surface (i.e., the first layer encountered by the air streamduring use).

In certain embodiments, the melt-blown filter layer includes a compositeof multiple layers of melt-blown fibers with larger fibers and more openstructure at a first major surface of the melt-blown composite andsmaller fibers and less open structure at a second major surface of themelt-blown composite. In certain embodiments of this construction, thesecond major surface of the melt-blown filter layer is adjacent thesupport layer and the first major surface is positioned as the mostupstream surface (i.e., the first layer encountered by the air streamduring use).

In certain embodiments, the melt-blown filter layer has a basis weightof up to 50 grams/meter² (g/m² or “gsm”), and often up to 100 gsm. Incertain embodiments, the melt-blown filter layer has a basis weight ofat least 5 grams/meter² (g/m² or “gsm”), and often at least 10 gsm.

The melt-blown filter layer is typically considered a depth filtrationlayer. As such, dirt is captured throughout the thickness of themelt-blown filter layer (i.e., in the “z” direction) as opposed to onthe surface of a surface loading filter media.

In certain embodiments, the melt-blown filter layer is at least 0.005inch (125 microns) thick, and often at least 0.01 inch (250 microns)thick. In certain embodiments, the melt-blown filter layer is up to 0.02inch (500 microns) thick.

In certain embodiments, the melt-blown filter layer has a Frazierpermeability (differential pressure set at 0.5 inch of water) of atleast 20 liters/meters squared-second (1/m²/sec), or at least801/m²-sec, or at least 2001/m²-sec when evaluated separately from theremainder of the construction. In certain embodiments, the melt-blownfilter layer has a Frazier permeability (differential pressure set at0.5 inch of water) of up to 10001/m²-sec, or up to 6001/m²-sec, whenevaluated separately from the remainder of the construction.

In certain embodiments, the electrostatically charged melt-blown filterlayer of the filter media of the present disclosure is a high-efficiencyfilter layer. In certain embodiments, an electrostatically chargedmelt-blown filter layer displays a filtration efficiency of at least 50%with 0.4-micron size DEHS (di-ethyl-hexyl-sebacat) particles at itsrated velocity. Preferably, the filtration efficiency is at least 65%,or at least 85%, or at least 95%, or at least 99.5%, or at least 99.95%of 0.4-micron size or the most penetrating particle size particles. Incertain embodiments, if not electrostatically charged, a melt-blownfilter layer displays a filtration efficiency of at least 10% with0.4-micron size DEHS (di-ethyl-hexyl-sebacat) particles at its ratedvelocity.

The melt-blown fibers can be prepared from a variety of polymers thatare suitable for being melt blown. Examples include polyolefins(particularly polypropylene), ethylene-chloro-trifluoro-ethylene, otherhydrophobic polymers, or non-hydrophobic polymers (e.g., polybutyleneterephthalate, polystyrene, polylactic acid, polycarbonate, nylon,polyphenylene sulfide) with a hydrophobic coating or additive, orcombinations thereof (e.g., blends or copolymers). Preferred polymersare polyolefins such as polypropylene, polyethylene, and polybutylene.Particularly preferred melt-blown fibers are made from polypropylene toenhance the watertight characteristics of a preferred filter medium ofthe present disclosure.

In certain embodiments, the melt-blown layer is hydrophobic. By this itis meant that the layer demonstrates a contact angle greater than 90degrees with water. The fibrous material of which it is made can behydrophobic (e.g., a polyolefin) or include a hydrophobic additive, orit can be coated with a hydrophobic material, such as the ones describedherein for the hydrophobic coating on the glass-containing layer, or itcan be treated with a plasma treatment technique.

Glass-Containing Filter Layer

In certain embodiments, the glass-containing filter layer includes glassfibers having an average diameter of less than 2 micron, and in certainembodiments less than 1 micron. In certain embodiments, the glass fibershave an average diameter of at least 0.01 micron, in certain embodimentsat least 0.1 micron.

The glass-containing filter layer may also include fibers other than theglass-containing fibers. For example, it may contain multi-componentfibers, typically bicomponent fibers, that function as binder fibers. Apreferred example is bicomponent binder fibers that are core-sheathfibers having a low melting point polyester sheath and a higher meltingpoint polyester core. The bicomponent fibers typically have fiberdiameters of at least 10 microns.

The glass-containing filter layer may also include polyester fibersother than the multi-component fibers. Preferred glass-containing filterlayers of the present disclosure include only glass fibers andbicomponent binder fibers.

Such fibers may be made by a variety of processes. In certainembodiments, the glass-containing filter layer is created using awet-laid process.

Although the binder fibers in the glass-containing filter layer are usedto avoid the use of any binder resin, such resin can be added to furtherimprove its strength. Examples of suitable binder resins includesolvent-based or water-basedlatex resins, water-based styrene acrylics,solvent-based phenolics, and solvent-based non-phenolics, such as thatavailable under the tradename HYCAR 26138 from Lubrizol of Cleveland,Ohio Typically, if used, a binder resin could be present in theglass-containing layer in an amount of up to 1 wt-%, up to 5 wt-%, or upto 10 wt-%, based on the total weight of the glass-containing filterlayer. Preferably, no binder resin is used in the glass-containing layer(or in any of the layers of the filter media).

Examples of suitable glass-containing filter layers include thosedescribed in U.S. Pat. Nos. 7,309,372, 7,314,497, 7,985,344, 8,057,567,and 8,268,033, and U.S. Publication Nos. 2006/0242933 and 2008/0245037.

In certain embodiments, the glass-containing filter layer has arelatively low compressibility. Typically, a glass-containing filterlayer has a compressibility of less than 40 percent at a pressure of17.6 pounds per square inch (psi) (i.e., 1.24 kg/cm²). In certainembodiments, a glass-containing filter layer of the present disclosurehas a compressibility of at least 20 percent at a pressure of 17 psi(i.e., 1.24 kg/cm²).

In certain embodiments, the glass-containing filter layer has arelatively low solidity. Typically, a glass-containing filter layer hasa solidity of less than 20 percent (%) at a pressure of 1.5 psi (i.e.,0.1 kg/cm²), often less than 15%. In certain embodiments, aglass-containing filter layer of the present disclosure has a solidityof at least 5 percent at a pressure of 1.5 psi (i.e., 0.1 kg/cm²).

In certain embodiments, the glass-containing filter layer has a basisweight of up to 70 grams/meter² (g/m² or “gsm”), and often up to 100gsm. In certain embodiments, the glass-containing filter layer has abasis weight of at least 20 grams/meter² (g/m² or “gsm”), and often atleast 30 gsm.

The glass-containing filter layer is considered a depth filtrationlayer. As such, dirt is captured throughout the thickness of themelt-blown filter layer (i.e., in the “z” direction) as opposed to onthe surface of a surface loading filter media. The salt loading capacityof the glass-containing filter layer is at least 10 grams/m² at ratedflow to 3 inches of water (750 Pa) terminal pressure drop.

In certain embodiments, the glass-containing filter layer is at least0.005 inch (125 microns) thick. In certain embodiments, theglass-containing filter layer is up to 0.02 inch (500 microns) thick.

In certain embodiments, the glass-containing filter layer has a Frazierpermeability (differential pressure set at 0.5 inch of water) of atleast 81/m²/sec, or at least 201/m²/sec, or at least 401/m²/sec, whenevaluated separately from the remainder of the construction. In certainembodiments, the glass-containing filter layer has a Frazierpermeability (differential pressure set at 0.5 inch of water) of up to4001/m²-sec, or up to 2001/m²/sec, when evaluated separately from theremainder of the construction.

In certain embodiments, and glass-containing filter layer of the filtermedia of the present disclosure is a high-efficiency filter layer. Incertain embodiments, a glass-containing filter layer displays afiltration efficiency of at least 70% with 0.4-micron size DEHS(di-ethyl-hexyl-sebacat) particles at its rated velocity. Preferably,the filtration efficiency is at least 85%, or at least 95%, or at least99.5%, or at least 99.95%, or at least 99.995% of the most penetratingparticle size (MPPS) particles at its rated velocity.

In certain embodiments, to enhance watertight characteristics, theglass-containing layer is coated with a hydrophobic coating. Suchhydrophobic coating includes a material that has little or no affinityfor water, or completely repels water, and thereby prevents or restrictswater from passing through the filter media. Typically, the hydrophobiccoating demonstrates a contact angle greater than 90 degrees when testedwith water. Examples of materials suitable for forming a hydrophobiccoating on the glass-containing layer include fluorochemicals,particularly fluoropolymers as described in U.S. Pat. No. 6,196,708.

Examples of useful fluoropolymers include those having a fluoroalkylportion or, preferably, a perfluoroalkyl portion. These fluoropolymersinclude, for example, fluoroalkyl esters, fluoroalkyl ethers,fluoroalkyl amides, and fluoroalkyl urethanes. Often, the fluoroalkyland/or perfluoroalkyl portion extends from a backbone of the polymer.

The fluoropolymers may include a variety of monomer units, Exemplarymonomer units include, for example, fluoroalkyl acrylates, fluoroalkylmethacrylates, fluoroalkyl aryl urethanes, fluoroalkyl allyl urethanes,fluoroalkyl maleic acid esters, fluoroalkyl urethane acrylates,fluoroalkyl amides, fluoroalkyl sulfonamide acrylates, and the like. Thefluoropolymers may optionally have additional non-fluoro monomer unitsincluding, for example, unsaturated hydrocarbons (e.g., olefins),acrylates, and methacrylates. Additional examples of suitablefluoropolymers are provided in U.S. Pat. No. 3,341,497.

Commercially available fluoropolymers include those available under thetrade designation OLEOPHOBOL CPX from Huntsman (Charlotte, N.C.), aswell as 3M Protective Material PM-490 (a nonionic fluorochemical resin),3M Protective Material PM-3633 (a fluoropolymer emulsion), 3M L-21484 (afluorinated amino salt derivative that can be diluted in water or polarorganic solvents), all of which are available from 3M Co. (St. Paul,Minn.).

Other exemplary, commercially available, fluoropolymers are provided inaqueous emulsions. The fluoropolymers can be extracted from the aqueousemulsion by removal of the water carrier. The fluoropolymers can then besolvated in an organic solvent. To facilitate the solvation of thefluoropolymer, a compound, such as acetone, can be optionally added tothe aqueous emulsion to break the emulsion. In addition, the particlesof fluoropolymer can be optionally ground, subsequent to removal ofwater make solvation easier and quicker.

Methods of coating such material on the glass-containing layer areconventional and well known to those skilled in the art. A typicalcoating weight is at least 0.5 wt-% and often no more than 3 wt-%.

Alternative to a hydrophobic coating, the glass-containing filter layercan be treated with a plasma treatment method to render it hydrophobic.

Support Layer

Filter media of the present disclosure may include a support layer. Thesupport layer can be of any of a variety of porous materials, includingfibrous materials, metal mesh, etc. Typically, fibrous materials usedfor the support layer are made of natural fiber and/or synthetic fibers.

In certain embodiments, the support layer includes fibers having anaverage diameter of at least 5 microns, or at least 10 microns. Incertain embodiments, the support layer can include fibers having anaverage diameter of up to 250 microns.

In certain embodiments, the support layer has a basis weight of at least50 grams/meter² (g/m² or “gsm”), and often at least 100 gsm. In certainembodiments, the support layer has a basis weight of up to 150grams/meter² (g/m² or “gsm”), and often up to 260 gsm.

In certain embodiments, the support layer is at least 0.005 inch (125microns) thick, and often at least 0.01 inch (250 microns) thick. Incertain embodiments, the support layer is up to 0.03 inch (750 microns)thick.

In certain embodiments, the support layer has a Frazier permeability(differential pressure set at 0.5 inch of water) of at least2001/m²-sec, when evaluated separately from the remainder of theconstruction. In certain embodiments, the support layer has a Frazierpermeability (differential pressure set at 0.5 inch of water) of up to80001/m²-sec, when evaluated separately from the remainder of theconstruction.

In certain embodiments, the support layer has a Gurley stiffness of atleast 100 grams, and often at least 300 grams. In certain embodiments,the support layer can have a Gurley stiffness of up to 10,000 grams. Amethod for measuring Gurley stiffness is described in TAPPI No. T543.

Examples of suitable material for the support layer (i.e., substrate)include spunbond, wetlaid, carded, or melt-blown nonwoven. Suitablefibers can be cellulosic fiber, glass fibers, metal fibers, or syntheticpolymeric fibers or the combination. Fibers can be in the form of wovensor nonwovens. Plastic or metal screen-like materials both extruded andhole punched, are other examples of filter substrates. Examples ofsynthetic nonwovens include polyester nonwovens, nylon nonwovens,polyolefin (e.g., polypropylene) nonwovens, polycarbonate nonwovens, orblended or multicomponent nonwovens thereof. Sheet-like substrates(e.g., cellulosic, synthetic, and/or glass or combination webs) aretypical examples of filter substrates. Other preferred examples ofsuitable substrates include polyester or bicomponent polyester fibers(as described herein for the glass-containing layer) orpolypropylene/polyethylene terephthalate, or polyethylene/polyethyleneterephthalate bicomponent fibers in a spunbond.

In certain embodiments, the support layer is a spunbond made of 100%polyester as pattern bonded continuous fiber with a high strength toweight ratio, sold under the tradename FINON and available from Kolonindustries.

In certain embodiments, the support layer is hydrophobic. The fibrousmaterial of which it is made can be hydrophobic (e.g., a polyolefin) orinclude a hydrophobic additive, or it can be coated with a hydrophobicmaterial, such as the ones described herein for the hydrophobic coatingon the glass-containing layer, or it can be treated with a plasmatreatment technique. Alternatively, if wet-laid, a hydrophobic resin canbe applied during the wet-laid process.

Filter Elements and Uses

The filter media of the present disclosure can then be manufactured intofilter elements (i.e., filtration elements), including, e.g., flat-panelfilters, cartridge filters, or other filtration components. Examples ofsuch filter elements are described in U.S. Pat. Nos. 6,746,517;6,673,136; 6,800,117; 6,875,256; 6,716,274; and 7,316,723.

The filter media can be corrugated. Exemplary corrugations are at adepth of 0.020 to 0.035 inch (0.5 mm to 0.9 mm). Corrugated filter mediacan then typically be pleated to form a pleat pack, then placed andsealed into a housing, as is known in the art.

Filter elements of the present disclosure can be used in industrialfiltration such as in dust collectors, and in commercial and residentialHVAC systems. Filter elements of the present disclosure are particularlyuseful in a gas turbine air intake system. Sue filtration systems aredescribed in M. Wilcox et al., “Technology Review of Modern Gas TurbineInlet Filtration Systems,” International Journal of Rotating Machinery,Volume 2012, Article ID 128134. An exemplary system is depicted in U.S.Patent Publication No. 2013/0008313. Filter elements of the presentdisclosure can also be used in filter systems commonly used today thatare highly complex and of multi-stage or “cascade” type.

FIGS. 4-14 depict various embodiments of filter elements of the presentdisclosure that are usable in gas turbine air intake systems.

A gas turbine system uses large amount of air, so the quality of airinto the system is important for the operation, performance, and life ofthe gas turbine. An inlet air filtration system is important to keep theair clean going into the gas turbine. Contaminated intake air can causeerosion, fouling, corrosion, and cooling air passage plugging. Thefiltration systems need to not only take out dry particulates, it alsoneed to stop liquid particles and to prevent delinquent salt gettingthrough when the moisture is high, or in other wet environments. So ahigh efficiency and watertight filter element is desired for modern gasturbine systems.

In FIG. 4, a pleated panel element 200 is shown in perspective view. Thepanel element 200 includes a media pack 202 of pleated media 204. Thepleated media 204 can comprise the filter medium described herein (e.g.,a melt-blown layer and a glass-containing layer). In the embodimentshown, the media pack 202 is held within a frame 206, with the examplesshown being a rectangular frame 206. The frame 206 typically willinclude a gasket (not shown) for permitting the element 200 to be sealedagainst a tube sheet in the intake system. In FIG. 4, the upstream sideof the pleated media 204 with the melt-blown layer is shown at 205 onthe same side as the incoming air shown at arrow 207. The cleaned air isshown at arrow 208, and emerges from the media 204 from a downstreamside of the media.

FIG. 5 depicts a perspective view of pocket filter element 210. Thepocket element 210 includes a layer of filter media 212 that cancomprise a filter medium of the present disclosure. In the embodimentshown, the pocket element 210 includes a plurality of panel pairs 213,214, with each panel pair 213, 214 forming a V-like shape. The filtermedia 212 is secured to a frame 216. The frame 216 typically will carrya gasket for allowing the pocket element 210 to be sealed against a tubesheet, such as tube sheet 38. In such an arrangement, the media 212 hasan upstream melt-blown side 217, which is inside of the V's, and adownstream side 218, which is on the outside of the V's.

FIGS. 6-8 depict views of a mini-pleat or multi-V style element 220. Theelement 220 includes a frame 222 holding a filter media pack 224 (FIG.8). The media pack 224 comprises a plurality of mini-pleats. Themini-pleats are arranged in a panel 226, and the element 220 includes aplurality of mini-pleated panel pairs 227, 228 (FIG. 6) of the media ofthe invention, each forming a V-like shape. In FIG. 6, the panel pairs227, 228 are shown in hidden lines, since the top portion of the frame222 obstructs the view of the panel pairs 227, 228. The frame 222defines a plurality of dirty air inlets 229 (FIG. 7), which leads to theinside part of each V of each pleated panel pair 227, 228. Each pleatedpanel pair 227, 228 includes an upstream side 230, which is on theinside of the V, and a downstream side 231, which is on the outside ofthe V.

FIGS. 9-14 show various embodiments of tubular, pleated filter elements.FIG. 9 shows a cylindrical pleated element 240 having a media pack 242that can include a filter medium of the present disclosure with anupstream side 244 and a downstream side 246. The downstream side 246 isinside of the interior volume of the element 240.

FIG. 10 depicts two of the cylindrical elements 240 axially aligned,such that they are stacked end to end.

In FIG. 11, cylindrical element 240 is axially aligned with a partiallyconical element 250. The partially conical element 250 is a tubularelement having a media pack 252 that can include a filter medium of thepresent disclosure. The element has an upstream side 254 and adownstream side 256. The conical element 250 has a first end 258 havinga diameter that matches the diameter of the cylindrical element 240. Theconical element 250 includes a second end 260 having a diameter that islarger than the diameter of the first end 258, thus forming the partialcone.

FIG. 12 depicts two partially conical elements 270, 280 arrangedaxially, and engaged end to end. Each of the elements 270 includes amedia pack 272, 282 forming a tube that can include a filter medium ofthe present disclosure. The media packs 272, 282 each have an upstreamside 274, 284 and a downstream side 276, 286.

FIG. 13 shows a single conical element 270. The element 270 can be usedalone installed in the intake system for a gas turbine without beinginstalled in element pairs, as shown in FIGS. 11 and 12.

FIG. 14 is another embodiment of a filter element 290 having media pack292 that can include a filter medium of the present disclosure. Themedia pack 292 is pleated and forms a tubular shape. In this embodiment,the tubular shape is an oval shape, and in one example embodiment, aratio of the short axis compared to the long axis of the oval is about0.7-0,9. The media 292 includes an upstream side 294 and a downstreamside 296.

It should be understood that each of the filter elements characterizedabove and depicted in FIGS. 4-14 can be flat media or corrugated mediaand/or operably installed in an intake system for a gas turbine or otherventilation system.

In operation, air to be filtered will be directed through the upstreamside, typically the melt-blown layer and then through the downstreamside of filter media in the respective filter element typicallyinstalled in a tube sheet. The filter media will remove at least some ofthe particulate from the air stream. After passing through thedownstream side of the media, the filtered air is then directed to thegas turbine.

FIGS. 15-18 exemplify a filtration system for a gas turbine orcompressor air intake that can include filter media and elements of thepresent disclosure. The system includes a hood arrangement; a louverarrangement, downstream of the hood arrangement; a coalescerarrangement, downstream of the louver arrangement; and a final stageincluding an arrangement of water-tight filters downstream of thecoalescer arrangement. The system is free of water removal stagesdownstream of the final stage. In one aspect, the coalescer arrangementincludes a plurality of panel filter elements. In one aspect, theplurality of panel filter elements is angled relative to each other in azigzag pattern. In one aspect, the panel filter element is comprised ofmesh. In certain embodiments, the mesh is metal. In one aspect, thepanel filter elements comprise depth loading filter media. In oneaspect, the panel filter elements comprise pleated filter media. In oneaspect, the panel filter elements could be watertight.

In one aspect, the watertight filters are pleated. In one aspect, thewatertight filters form a wave or other shape. In one aspect, thewatertight filters are mounted relative to a horizontal at a slope of1-25 degrees to slope in a downward direction upstream.

With respect to the embodiments exemplified in FIGS. 15-18, in anotheraspect, a method for filtering air through a system for a gas turbine isprovided. The method includes directing air to be filtered into a hoodarrangement; from the hood arrangement, directing the air into a louverarrangement; from the louver arrangement, directing the air into acoalescer arrangement; and from the coalescer arrangement, directing theair into a final stage including arrangement of watertight filtersand/or any form of static filters. The system is free of water removalstages downstream of the final stage. In one aspect, the method ofdirecting air to be filtered into a hood arrangement includes directingair having a velocity of no greater than 4.5 meters per second (m/s)through the hood arrangement at a pressure drop less than 100 Pa. Inanother aspect, the step of directing air into a louver arrangementincludes directing air having a velocity of no greater than 5.6 m/sthrough the hood arrangement at a pressure drop less than 60 Pa.

In another aspect, the step of directing air into a coalescerarrangement includes directing air having a media velocity of no greaterthan 3.0 m/s through the coalescer arrangement at a pressure drop lessthan 175 Pa. In another aspect, the step of directing air into anarrangement of watertight filters includes directing air having a mediavelocity of no greater than 0.2 m/s through the arrangement ofwatertight filters at a pressure drop less than 375 Pa. In anotheraspect, the method includes during the step of directing air into anarrangement of watertight filters, allowing liquid to drain by gravityfrom the watertight filters on an upstream side of the watertightfilters.

More specifically, with reference to FIG. 15, a filtration system 10 fora gas turbine or compressor air intake is provided. The gas turbine mayhave an approximate size equivalent to a Rolls Royce RB211 turbine,which is about 5673 m³/min (200,335 cfm). This turbine has a combustionair flow of about 4560 m³/min (161,035 cfm), and a ventilation air flowof about 113 m³/min (39,300 cfm). Alternate turbine sizes can be usedwith higher or lower air flow rates.

Air to be filtered is shown at arrows 14. The air passes through thesystem 10, filters it, and it then enters an inlet duct 18. The cleanedair, shown at arrows 15 then travel toward the gas turbine to provide asupply of combustible air to the gas turbine, which is significantlyfree of particles and aqueous solutions that could lead to damage oraccumulation of corrosive deposits on the gas turbine.

The system 10 includes a filter house module 16. The filter house module16 serves as an entry point for air to be filtered in the system 10. Assuch, the air flow at arrows 14 initially passes through the filterhouse module 16 on its way toward the gas turbine. The filter housemodule 16 may be serviced by an operator through an access point 20.

The filter housing module can include a hood arrangement 22. The hoodarrangement 22 can be part of a stage 0 of the system 10. The hoodarrangement 22 will typically include a plurality of weather hoods 24 toprovide for protection against rain and snow. The hoods 24 are typicallysloped to help foster drainage of any water collected on the hoods 24.As can be seen in FIG. 15, the hoods 24 are sloped downward in adirection upstream of the rest of the system 10, so that any collectedwater will be drained outside of the filter module 16 and system 10.

Typically, air 14 entering the hood arrangement 22 will have an entrancevelocity of no greater than 4.5 m/s (886 fpm). The pressure drop acrossthe weather hoods 24 will be less than 100 Pa (0.40 inch of water).

Downstream of the hood arrangement 22 is a louver arrangement 26. Thelouver arrangement 26 is part of a first stage, which is the stageencountered by the air entering the system 10 after the stage 0 hoodarrangement 22. The louver arrangement 26 is provided to further fosteror encourage coalescing and collection of water particles in the air. Inpreferred embodiments, the louver arrangement 26 will include stainlesssteel (or other materials) louvers 28. The air that enters the louverarrangement 26 will typically have a velocity of no greater than 5.6 m/s(1102 fpm). This higher velocity encourages inertial removal of water.The pressure drop across the louver arrangement 26 will typically beless than 57 Pa (0.23 inch of water).

Downstream of the first stage louver arrangement 26, a coalescerarrangement 42 may be provided as a second stage. The coalescerarrangement 42 has two primary operational modes. The first one of theseoperational modes includes the coalescer arrangement 42 removingrelatively small aerosol droplets, such as salt aerosol droplets, fromthe air coming in at arrow 14. These small aerosol droplets arecoalesced into larger aerosol droplets, for example, the droplets can begreater than about 20 microns in diameter. This coalescing processallows for drainage of a relatively large portion of liquid, such assalt water, rain, fog, mist, condensate, out and away from the air flow14.

A second one of the operational modes of the coalescer arrangement 42includes serving as a pre-filter. When serving as a pre-filter, thecoalescer arrangement 42 has an efficiency of which may be such that thecoalescer arrangement 42 captures and/or removes solid coarseparticulates, including, for example, a majority of particulates havingdiameters of more than 1 micron, in some embodiments more than 3microns, and in some embodiments, more than 5 microns, from the air flow14. The coalescer arrangement 42, therefore, serves to extend theservice life of the stages that are downstream of the coalescerarrangement 42.

The coalescer arrangement 42 can include a plurality of panel filterelements 44. Preferably, and in reference to FIG. 16, the panel filterelements 44 can be angled relative to each other in a zigzag arrangement46. The zigzag arrangement 46 increases the amount of coalescing mediaarea available by at least 33%, as compared to an arrangement that wasnot zigzagged and merely straight or flat. The zigzag arrangement 46also helps to reduce media velocity through the coalescer arrangement 42by at least 33%. This also helps to increase water removal efficiencyfor finer mists/aerosols.

In one example, the panel filter elements 44 comprise a mesh, such as astainless steel mesh panel filter 48. Alternatives to the stainlesssteel panel filter 48 include a panel filter of a depth loading filtermedia, such as a meltblown media. The panel filter elements may alsocomprise pleated filter media and/or a watertight element. Methods ofmeasuring the watertight characteristics of a filter element include,for example, the test described in International Publication No. WO2012/034971, and in the Examples Section.

The coalescer arrangement 42 could be provided as a combinedcoalescer/prefilter, as one product, or a separate coalescer and aseparate pre-filter, as possible or desired.

Downstream of the coalescer arrangement 42 is a final stage including anarrangement of watertight filters 50. The arrangement of watertightfilters 50 prevents liquid or aqueous solutions of deliquesced ordissolved particles or dry/solid salt particles from the coalescerarrangement 42 that may have been re-released into the airflow and whichalso removes fine dry/solid particles from the air flow.

In preferred arrangements, the arrangement of watertight filters 50 ismounted at an angle to slope toward a direction of the incoming air 14.If the system 10 is on a relatively horizontal ground, the watertightfilters 50 are mounted at an angle to slope in a downward directionupstream. A useful range of angles includes a slope between 1-25°, forexample, about 10°. In some embodiments, the range of angles includes aslope between 5-15°. In this manner, any water or liquid captured by thewatertight filters 50 is caused to drain by gravity into the upstreamsection of the system 10.

The watertight filter arrangement 50 has a filtration efficiency toremove both the dust particulates that penetrate the stages upstream toit and any fine dry salt particulates in the atmosphere from the airflow 14. In certain embodiments, the watertight filter arrangement 50has an average filtration efficiency of greater 95% and/or a minimumfiltration efficiency of at least 70%, as measured by European StandardEN 779 (April 2012).

In one example arrangement, shown in FIG. 17, the watertight filters 50are pleated filters 53. In preferred arrangements, the watertightfilters pleated filters 53 have a media pack 30 forming a wave shape 54forming a wave-shaped filter element 56. One example filter element 56that can be utilized is described in U.S. Patent Publication No.2011/0067368.

In FIG. 17, the media pack 30 has a first end 32 a and an oppositesecond end at 32 b. The media pack 30 includes a first lateral side 33 aand a second lateral side 33 b (FIG. 18). The first and second lateralsides 33 a, 33 b extend between the first and second opposite ends 32 a,32 b. The media pack 30 can be constructed from a single section ofseamless pleated media having a plurality of pleats 34 (FIG. 18). Thepleats 34 are shown schematically in FIG. 18, and are not shown in FIG.17 for purposes of clarity. As shown, the pleats 34 are longitudinallyoriented such that the pleats 34 extend from the first and secondopposite ends 32 a, 32 b and define the width of the media pack 30.

The media pack 30 can also be constructed with a structural or safetyscreen 80 on the upstream or downstream side 31 a, 31 b of the pleats34. In FIG. 18, the media pack 30 has a cross section defined betweenthe first and second lateral sides 33 a, 33 b. The cross sectionincludes a plurality of outward projections 35, and in the embodimentshown, three outward projections 35. The media pack 30 can also have aninward recess 36, and as shown in the example in FIG. 18, has two inwardrecesses 36.

The outward projections 35 and inward recesses 36 define an internalradius r. As constructed, media pack 30 is fanned around each radiussuch that a plurality of pleats 34 extends around each internal radius“r”. In typical installations, the number of pleats 34 that extendaround the internal radius “r” will be from 2 to 80 pleats, for example,25 to 50 pleats. The internal radius “r” can be about 0.25 inch and upto about 4 inches, preferably between 0.6 inch and 0.9 inch, and mostpreferably about 0.75 inch. The internal radius can vary in otherembodiments, as can the number of pleats per inch.

By use of the term “wave shape” to describe the example watertightpleated filter 53 shown in FIG. 17, it is meant that the cross sectionof media pack 30 has a shape including oppositely curved sections at theinward recesses 36 and outward projections 35 that are separated byeither straight or curved sections of media pack 30.

In the embodiment shown in FIG. 17, the element 56 includes a first endcap 40 and a second end cap 52. End caps 40, 52 are for providingstructural support for the filter element 50, for retaining thecross-sectional shape of the filter element 56, and for ensuring thatthe air to be filtered passes through the media pack 30 before travelingdownstream to the intake system of the gas turbine.

In FIG. 17, the first end cap 40 is secured to the first end 32 a, whilethe second end cap 52 is secured to the second end 32 b of the mediapack 30.

In the embodiment of FIG. 17, the filter element 56 includes a framemember 60. The frame member 60 holds a gasket 70, which is provided toform a seal against a tube sheet or other mounting surface in the filterhouse module 16 of the system 10.

Other embodiments of watertight filters 50 can be used, in addition tothe example shown in FIGS. 17 and 18. Examples include mini-pleats,panel filters, bag filters, static cylindrical cartridge filters, etc.The watertight filters 50 used will typically have an airflow per filterelement of about 70.9 m³/min (2504 cfm). The watertight filters 50 wouldhave a pressure drop less than 375 Pa (1.50 inch of water). The mediavelocity of the air through the watertight filters 50 will typically beno greater than 0.2 m/s (40 fpm).

A useful arrangement of watertight filters 50 will typically include thefollowing characteristics: a media area of between 300 and 320 sq. ft.;a rated air flow of 2500 cfm (synthetic filter media); a depth in inchesof no greater than 20, typically 16-19 inches; about 75-85 individualfilter elements; a media velocity in feet per minute of under 10 fpm;and a media velocity of less than 3 m/min, and typically 2-3 m/min.

One advantage of the system 10 is that due to the performance of thevarious stages described, the system 10 is free of water removal stagesdownstream of the final stage of watertight filters 50. There are nofurther water removal stages necessary downstream of the watertightfilters 50. In certain embodiments, the system includes at least onestage (typically the coalescer arrangement and/or the watertight filterstage), wherein the inlet velocity per media area (or other inlet stagesurface) is decreased relative to the previous stage. The actual inletvelocities to the media or surface of a stage will be determined by suchparameters as inlet size and fluid flow rate.

Another of the advantages of the filtration system 10 is that aperimeter footprint of the system as viewed from the top (i.e., the viewof FIG. 16) may be smaller as compared to prior art systems.Conventional low velocity systems would typically have a largerfootprint to achieve the same performance as the disclosed system.

The system 10 can be utilized for a method for filtering air for a gasturbine. The method includes directed air to be filtered into a hoodarrangement. This includes, for example, air 14 being directed into thehood arrangement 22. This would typically include having the air at avelocity of no greater than 4.5 m/s through the hood arrangement 22 at apressure drop of less than 100 Pa. The hood arrangement 22 will help toshelter the incoming air 14 from rain or snow, for example.

The method can include, from the hood arrangement, directing the airinto a louver arrangement. For example, this can include directing theair from hood arrangement 22 into louver arrangement 26. The air wouldbe at a velocity of no greater than 5.6 m/s through the louverarrangement 26 at a pressure drop less than 60 Pa. The louverarrangement 26 can include louvers 28 to help coalesce water dropletsinto larger droplets and encourage draining of the liquid from the air.

The method can include directing the air from the louver arrangement andinto a coalescer arrangement. For example, this can include directingthe air from louver arrangement 26 into coalescer arrangement 42. Thiscan include directing the air having a media velocity no greater than3.0 m/s through the coalescer arrangement 42 at a pressure drop lessthan 175 Pa. This may also include directing the air through a pluralityof panel filter elements 44. It may also include directing the airthrough panel filter elements 44 angled relative to each other in azigzag arrangement 46. The panel filter elements 44 can include mesh, ordepth loading filter media (such as meltblown media), or pleated filtermedia, or some combination. This step helps to further coalesce liquiddroplets and help remove liquid from the air. It will also remove fineparticulate.

The method can also include from the coalescer arrangement, directingthe air into a final stage including an arrangement of watertightfilters. For example, this can include directing the air from thecoalescer arrangement 42 into watertight filters 50. This may furtherinclude directed the air having a media velocity of no greater than 0.2m/s through the arrangement 50 at a pressure drop less than 375 Pa.

In one example, this step can include directing the air into anarrangement of pleated watertight filters having a wave shape, such asfilter element 56.

During the step of directing air into the arrangement of watertightfilters, there can further be a step of allowing liquid to drain bygravity from the watertight filters on an upstream side of thewatertight filters 50.

The method of filtering air through the system 10 is free of waterremoval stages downstream of the final stage of watertight filters 50.

The above specification, examples and data provide a completedescription of principles. Many embodiments can be made applying theseprinciples.

EXEMPLARY EMBODIMENTS

1. An air filter medium comprising:

-   -   a melt-blown filter layer comprising melt-blown fibers; and    -   a high-efficiency glass-containing filter layer comprising glass        fibers and multi-component binder fibers; and    -   an optional support layer;    -   wherein the layers are configured and arranged for placement in        an air stream.        2. The filter medium of embodiment 1 wherein the melt-blown        fibers have an average diameter of greater than 1.5 microns.        3. The filter medium of embodiment 1 or 2 wherein the melt-blown        filter layer has a compressibility of greater than 40% at a        pressure of 1.24 kg/cm².        4. The filter medium of any of embodiments 1 through 3 wherein        the melt-blown filter layer is hydrophobic.        5. The filter medium of any of embodiments 1 through 4 wherein        the melt-blown filter layer is the most upstream layer.        6. A filter medium comprising:    -   a melt-blown filter layer comprising melt-blown fibers having an        average diameter of greater than 1.5 microns; wherein the        melt-blown filter layer has a compressibility of greater than        40% at a pressure of 1.24 kg/cm²;    -   a high-efficiency glass-containing filter layer comprising glass        fibers and multi-component binder fibers; and    -   an optional support layer.        7. The filter medium of any of embodiments 1 through 6 wherein        the layers are adhered together with an adhesive, thermal        bonding, ultrasonic bonding, binder fibers, or a combination        thereof (preferably, an adhesive, binder fibers, or a        combination thereof).        8. The filter medium of embodiment 7 wherein the layers are        adhered together with a hot melt adhesive.        9. The filter medium of embodiment 8 wherein the adhesive forms        a continuous or patterned layer.        10. The filter medium of any of embodiments 1 through 9 wherein        the support layer is positioned between the melt-blown layer and        the glass-containing layer.        11. The filter medium of any of embodiments 1 through 9 wherein        the glass-containing layer is positioned between the melt-blown        layer and the support layer.        12. The filter medium of any of embodiments 1 through 11 wherein        the melt-blown filter layer is electrostatically charged.        13. The filter medium of any of embodiments 1 through 12 wherein        the melt-blown filter layer is hydrophobic and preferably        includes fibers comprising a polyolefin, polybutylene        terephthalate, polystyrene, ethylene-chloro-trifluoro-ethylene,        polylactic acid, polycarbonate, nylon, polyphenylene suphide, or        combinations thereof (preferably the fibers are hydrophobic and        include a polyolefin, ethylene-chloro-trifluoro-ethylene, or        combinations thereof).        14. The filter medium of embodiment 13 wherein the melt-blown        fibers comprise polyolefin fibers.        15. The filter medium of embodiment 14 wherein the melt-blown        fibers comprise polypropylene fibers.        16. The filter medium of any of embodiments 1 through 15 wherein        the melt-blown fibers have an average diameter of at least 2        microns.        17. The filter medium of embodiment 16 wherein the melt-blown        fibers have an average diameter of 2-3 microns.        18. The filter medium of any of embodiments 1 through 17 wherein        the melt-blown filter layer has a basis weight of 5-100 g/m².        19. The filter medium of embodiment 18 wherein the melt-blown        filter layer has a basis weight of 10-50 g/m².        20. The filter medium of any of embodiments 1 through 19 wherein        the melt-blown layer comprises a composite of multiple layers of        melt-blown fibers with larger fibers and more open structure at        a first major surface of the melt-blown composite and smaller        fibers and less open structure at a second major surface of the        melt-blown composite.        21. The filter medium of any of embodiments 1 through 20 wherein        the melt-blown layer comprises a continuously gradient structure        of larger fibers and more open structure at a first major        surface and smaller fibers and less open structure at a second        major surface.        22. The filter medium of embodiment 20 or 21 wherein the second        major surface is adjacent the support layer and the first major        surface is positioned as the most upstream surface.        23. The filter medium of any of embodiments 1 through 22 wherein        the glass-containing layer comprises up to 10 wt-% of a binder        resin, based on the total weight of the glass-containing layer.        24. The filter medium of any of embodiments 1 through 23 wherein        the melt-blown layer is 125-500 microns thick.        25. The filter medium of any of embodiments 1 through 24 wherein        the melt-blown layer has a Frazier permeability (differential        pressure set at 0.5 inch of water) of 20-10001/m²/sec) (or        20-600, or 80-1000, or 80-600, or 200-1000, or 200-6001/m²/sec).        26. The filter medium of any of embodiments 1 through 25 wherein        the melt-blown layer when electrostatically charged displays a        filtration efficiency of at least 70% with 0.4-micron size DEHS        (di-ethyl-hexyl-sebacat) particles at its rated velocity.        27. The filter medium of any of embodiments 1 through 26 wherein        the glass-containing filter layer has a basis weight of 20-100        g/m².        28. The filter medium of embodiment 27 wherein the        glass-containing filter layer has a basis weight of 30-70 g/m².        29. The filter medium of any of embodiments 1 through 28 wherein        the glass-containing filter layer has a compressibility of less        than 40 percent at a pressure of 1.24 kg/cm².        30. The filter medium of any of embodiments 1 through 29 wherein        the glass fibers have an average diameter of less than 2 microns        (and often less than 1 micron).        31. The filter medium of any of embodiments 1 through 30 wherein        the multi-component binder fibers of the glass-containing filter        layer comprise bicomponent fibers having a low melting point        polyester sheath and a high melting point polyester core.        32. The filter medium of any of embodiments 1 through 31 wherein        the glass-containing filter layer further comprises polyester        fibers distinct from the multi-component binder fibers.        33. The filter medium of any of embodiments 1 through 32 wherein        the glass-containing filter layer is created using a wet-laid        process.        34. The filter medium of any of embodiments 1 through 33 wherein        the glass-containing filter layer 125-500 microns thick.        35. The filter medium of any of embodiments 1 through 34 wherein        the glass-containing filter layer has a Frazier permeability        (differential pressure set at 0.5 inch of water) of        8-4001/m²/sec (or 8-200, or 20-400, or 20-2001/m²/sec).        36. The filter medium of any of embodiments 1 through 35 wherein        the glass-containing filter layer displays a filtration        efficiency of at least 70% with 0.4-micron size DEHS        (di-ethyl-hexyl-sebacat) particles at its rated velocity.        37. The filter medium of any of embodiments 1 through 36        comprising a support layer.        38. The filter medium of embodiment 37 wherein the support layer        comprises fibers having an average diameter of at least 5        microns (preferably, at least 10 microns).        39. The filter medium of embodiment 38 wherein the support layer        is a spunbond support layer.        40. The filter medium of any of embodiments 37 through 39        wherein the support layer has a Gurley stiffness of 100 grams or        more (preferably, 300 grams or more).        41. The filter medium of any of embodiments 37 through 40        wherein the support layer has a basis weight of 70-260 g/m².        42. The filter medium of any of embodiments 1 through 41 wherein        the glass-containing filter layer comprises a hydrophobic        coating.        43. The filter medium of embodiment 42 wherein the hydrophobic        coating comprises a fluorochemical.        44. The filter medium of any of embodiments 1 through 43 which        is corrugated.        45. The filter medium of any of embodiments 1 through 44 which        displays a hydrostatic head of at least 10 inches (25.4 cm) of        water (or at least 15 inches (38.1 cm) of water, or at least 20        inches (50.8 cm) of water).        46. The filter medium of any of embodiments 1 through 45 which        displays a filtration efficiency of at least 70% with 0.4-micron        size DEHS particles at its rated velocity.        47. The filter medium of any of embodiments 1 through 46 which        displays a filtration efficiency is at least 85% (or at least        95%, or at least 99.5%, or at least 99.95%, or at least 99.995%)        of the most penetrating particle size particles (MPPS) at its        rated velocity (i.e., rated flow rate).        48. The filter medium of any of embodiments 1 through 47 which        displays a salt loading capacity of at least 10 g/m².        49. The filter medium of any of embodiments 1 through 48        comprising two or more melt-blown filter layers.        50. The filter medium of any of embodiments 1 through 49        comprising two or more glass-containing filter layers.        51. A filter element comprising a housing and a filter medium of        any of embodiments 1 through 50.        52. The filter element of embodiment 51 wherein the filter        medium is pleated.        53. The filter element of any of embodiments 51 through 52 which        displays an efficiency of at least F9 per EN779:2012.        54. The filter element of embodiment 53 which displays an        efficiency of at least E10 per EN1822:2009.        55. The filter element of embodiment 54 which displays an        efficiency of at least E11 per EN1822:2009.        56. The filter element of any of embodiments 51 through 55 which        is watertight.        57. The filter element of any of embodiments 51 through 56 which        displays a dust loading capacity of at least 30 g/m² of ASHRAE        dust (per ASHRAE 52.2-2007 or EN779:2012) when loaded to 4        inches of water dp (i.e., 1000 Pa pressure drop) in static mode.        58. The filter element of any of embodiments 51 through 57        positioned in a gas turbine inlet system.        59. A method of filtering air, the method comprising directing        the air through a filter medium or filter element of any one of        embodiments 1 through 58.        60. A method of filtering air, the method comprising directing        the air through a filter medium comprising:    -   a melt-blown filter layer comprising melt-blown fibers;    -   a high-efficiency glass-containing filter layer comprising glass        fibers and multi-component binder fibers; and    -   a support layer;    -   wherein the melt-blown filter layer is the most upstream layer.

EXAMPLES

Objects and advantages of this disclosure are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

Test Methods Frazier Permeability Test

The permeability of the media was measure using a Frazier PermeabilityTester at 0.5 inch (in) H₂O (125 Pascals (Pa)) in accordance with ASTMD737.

Hydrostatic Head Test

This is to test the bulk water penetration through media. The tests areperformed using a TEXTEST FX3000 Hydrostatic Head tester II, but anytester that conforms to the standards AATCC 127, BS 2, 823, DIN 53,886,EDANA 120.1-80, INDA IST 80.4, ISO 811, ISO 1,420A, JIS L 1,092 B wouldbe acceptable. A sample that is at least 5.5 inches (14 cm) square isplaced in the tester with the upstream side face down and then clampedinto place. Water pressure is applied to the upstream side of the sampleat a gradually increasing value (a gradient of 60 mbar/min) until 3water droplets are seen on the downstream surface of the media. At thispoint the test is stopped and the terminal pressure is recorded.

Salt Loading Test

This is to test how much dust or particulate the media can capture andhold before it is plugged up. A TSI 3160 bench is used to load thefiltration media with salt and record the salt loaded, salt passed anddP across the media for a particular face velocity. The media is placedin the bench so that the airflow is the same as it would be in the realworld. The other settings for the bench are to be run to themanufacturer's standards. The amount of salt loaded at 2 inches (500 Pa)and 4 inches (1000 Pa) of water column is recorded.

Water Spray Test

This test is to evaluate how much the filter element can prevent waterdroplets getting through the element, so to test the watertightness ofthe element. A filter element is placed into a 24-inch×24-inch(61-cm×61-cm) duct. An SU4 nozzle is installed in the duct 64″ (163 cm)away and facing the element. The nozzle is centered horizontally withthe center of the element. A water rotometer is installed in the line tocontrol and monitor the water flow rate. Air is pulled through theelement using a pump so that the element(s) are run at their rated flowrate.

The water spray is generated by feeding 60 psi (413.7 kPa) of compressedair into the nozzle and the element was challenged with a water flowrate of 0.5-1 liter/minute. The test lasts 6 hours or more. The dPacross the element is recorded during the test. The water downstream ofthe element is collected and measured when the test is finished.

EN1822 Test

This is a European standard for high efficiency filter testing andclassification. A filter element is installed in an ASHRAE duct. Air ispulled through the element at the rated flow, and the element ischallenged with DEHS particles varying from 0.02 to 0.6 microns. Thenumber of particles of a particular size are measured upstream anddownstream of the filter using an SMPS and an APS, and 100×(1-downstream particles/upstream particles) equals the efficiency atthat particle size. The efficiency of the element is tested before andafter soaked in an IPA bath, to remove the electrostatic effects ifapplicable.

Dust Holding Capacity Test (DHC Test)

This test is to evaluate the filter life in a lab test condition. Afilter element is installed in an ASHRAE duct. Air flows through theelement(s) at the rated flow while ASHRAE dust is fed into the duct perEN779:2012 standard (except the final dP has been increased to 4 inches)or ASHRAE 52.2 standard. The pressure drop across the element(s) ismeasured and the amount of dust fed is recorded at the multiplepre-determined pressure drop points.

EN779:2012

In this standard a filter or filter pair is loaded into an ASHRAE duct.The element is then loaded progressively, with dust specified in ASHRAE52.2, while it is run at the manufacturers rated speed. The efficiencyof the element is measured at initial and at various stages ofprogressive loading. At 1.8 inches of W.C. (450 Pa) the test is stoppedand the amount of dust captured is recorded, which gives the dustholding capacity at that dP (DHC). The average efficiency of the elementis calculated by weight average of efficiency at various pressure droppoints. To classify the level of the element performance, a furtherefficiency test of a sheet of media is required after IPA soak, where asample of media like the one used in the element is soaked in 99.5% pureIPA for two minutes then dried for 24 hours. The sample is challengedwith DEHS particles at 100% of the face velocity the element would seeif it was run at the rated speed. The efficiency is recorded.

Example 1

Laminated filter media were prepared using the following technique. Aroll of 30 gsm polypropylene melt-blown filter material was purchasedfrom H&V of Floyd, Va. (Product Number PE13030CA, electrostaticallycharged as obtained from the supplier). A 42-gsm wet-laid filtermaterial that includes a mixture of glass and bicomponent PET fibers wasprepared similar to that of Example 6 in U.S. Pat. No. 7,314,497 (withthe modification that it consists of 40% B08 microglass fibers fromLauscha Fiber Interanational (Lauscha, Germany) and 60% TJ04BNbicomponent PET fibers from Teijin (Osaka, Japan)). A spunbond supportmaterial of 100 gsm of FINON C310NW was purchased from MidwestFiltration of Cincinnati, Ohio. The sheet properties are in Table 1.

TABLE 1 Properties of the components of Example 1 FINON Property UnitsPE13030CA C310NW EN929 Basis Weight lbs./3000 ft² 18.4 61.5 26 grams/m²30 100 42 Fiber Size μm 2.9 17.4 0.8/14 Thickness (1.5 pounds per squareInches 0.0101 0.008 0.0071 inch (psi)) Mm 0.257 0.203 0.183 FrazierPermeability @ 0.5 inches Fpm 47.5 108 22.4 (in) H₂O (125 Pascals (Pa))1/m²/sec 380 864 179 Hydrostatic Head Mbar 41.50 6.00 8.00 NO IPA MPPSDEHS efficiency 4 % 96.69 <10% 95.14 feet per minute (fpm) (2.0centimeters/ seconds (cm/s)) Post IPA soak MPPS DEHS efficiency % 40.21<10% 93.83 4 fpm (2.0 cm/s)

These three rolls were layered so that the melt-blown layer wasupstream, the wet-laid layer was in the middle, and the spunbond layerwas on the bottom. The three layers were heat laminated at 265° F. usinga copolyester hotmelt adhesive available under the tradename GRILTEX 9E,a granular adhesive from EMS-Griltech of Switzerland, at a rate of 4.07g/m² between each layer.

The material was then corrugated to an average depth of 0.0275 inches(0.699 mm) (measuring the distance in the z direction from the top ofthe peak to the bottom of the trough on the wire side of the media) with4.5 corrugations/inch (1.77 corrugations/cm). The flat sheet media waspleated at 2 inches (5.1 cm) pleat depth (with PLEATLOC separation) andbuilt into a 26×2 inch (66×2 cm) conical and cylindrical filter pair.The conical elements had 280 pleats per element while the cylindricalelements had 230. The elements were built such that the melt-blown layerwas facing upstream.

The laminated and corrugated media was tested for its flat sheetproperties, and the elements were tested for efficiency, waterrepellency and dust holding capacity (DHC) per EN1822, the Water SprayTest, and EN779:2012 respectively. The results are shown in Table 2.

TABLE 2 Properties of the laminated media and element Example 1 Example1 before after Property and test results Units corrugation corrugationBasis Weight lbs./3000 ft² 105.9 105.9 gram/m² 172.3 172.3 Thickness(1.5 psi) inches 0.0302 mm 0.767 Frazier Permeability @ 0.5 in fpm 13.6012.83 H₂O (125 Pa) l/m²/sec 108.8 102.6 Hydrostatic Head Mbar 91.3385.17 NO IPA MPPS DEHS efficiency % 99.56 99.73 4 fpm (2.0 cm/s) PostIPA soak MPPS DEHS efficiency % 91.68 91.66 4 fpm (2.0 cm/s) Flat sheetsalt loading at 4 inches and mg 158.00 180.00 3.6 fpm (62 cm²)Corrugation Depth inches — 0.0275 mm 0.6985 Element dP in. H₂O — 0.70 Pa175 Element Efficiency (pre IPA) % — 98.80 Element Efficiency (post IPA)% — 95.40 Element DHC at 4 in W.C. (1000 Pa) grams — 447 (cylindricalonly) Water Spray Test-final dP in. H₂O — 2 Pa 500 Water SprayTest-water downstream ml — 0

Example 2

Laminated filter media were prepared using the following technique. Aroll of polypropylene melt-blown filter material was purchased from H&Vof Floyd, Va. (Product Number PE13030CA, electrostatically charged asobtained from the supplier). A 55 gsm wet-laid filter material thatincludes a mixture of glass and bicomponent fibers was prepared similarto that of Example 6 in U.S. Pat. No. 7,314,497 (with the modificationthat it consists of 40% B08F microglass fibers from Lauscha FiberInternational (Lauscha, Germany) and 60% TJ04BN 2d×5 mm fibers fromTeijin (Osaka, Japan)). A spunbond support material of FINON C310NW waspurchased from Midwest Filtration of Cincinnati, Ohio. The sheetproperties are in Table 3.

TABLE 3 Properties of the components of Example 2 FINON Property UnitsPE13030CA C310NW EN1018 Basis Weight lbs./3000 ft² 18.4 61.5 34 grams/m²30 100 55 Fiber Size μm 2.9 17.4 0.8/14 Thickness (1.5 psi) Inches .0101.008 .0105 Mm 0.257 0.203 0.268 Frazier Permeability @ 0.5 Fpm 47.50 10816.5 in H₂O 1/m²/sec 380 864 132 Hydrostatic Head Mb 41.50 6.00 8.00 NOIPA MPPS DEHS efficiency % 96.69 <10% 92 4 fpm (2.0 cm/s) Post IPA soakMPPS DEHS % 40.21 <10% 89 efficiency 4 fpm (2.0 cm/s)

These three rolls of media were provided to JDX Nippon (Dalton, Ga.) forprocessing. The Layers were laminated with hot spray adhesive by JDZNippon with direction to use the minimum amount of adhesive possible.The layers were positioned such that the melt-blown layer was upstream,the spunbond layer was in the middle and the wet-laid media wasdownstream

The material was then corrugated to an average depth of 0.0265 inch(0.67 mm), (measuring the distance in the z direction from the top ofthe peak to the bottom of the trough on the wire side of the media) with4.5 corrugations per inch (1.77 corrugations/cm).

The flat sheet media was pleated at 2 inches (5.1 cm) pleat depth with(with PLEATLOC separation) and built into a 26-inch (66-cm) conical andcylindrical filter pair. The conical elements had 280 pleats per elementwhile the cylindrical elements had 230. The elements were built suchthat the melt-blown layer was facing upstream.

The laminated and corrugated media was tested for its flat sheetproperties, and the elements were tested for efficiency, waterrepellency and dust holding capacity using EN1822, the Water Spray Test,and the dust holding capacity test (DHC) using EN779:21012 respectively.The results are shown in Table 4.

TABLE 4 Properties of the laminated media and element Example 2 Example2 before after Property Units corrugation corrugation Basis Weightlbs./3000 ft² 113.9 113.9 grams/m² 185.4 185.4 Thickness (1.5 psi)inches 0.0275 — mm 0.699 — Frazier Permeability @ 0.5 in fpm 6.01 6.21H₂O (125 Pa) 1/m²/sec 48.1 49.7 Hydrostatic Head mb 61 70 NO IPA MPPSDEHS efficiency % 99.92 99.83 4 fpm (2.0 cm/s) Post IPA soak MPPS DEHS %96.37 94.32 efficiency 4 fpm (2.0 cm/s) Flat sheet salt loading at 4 in(1000 Pa) mg 71 102 and 3.6 fpm (1.8 cm/s) at 62 cm² Corrugation Depthinches — 0.0265 mm 0.673 Element dP in. H₂O — 0.80 Pa 200 ElementEfficiency (pre IPA) % — 99.52 Element Efficiency (post IPA) % — 95.80Element DHC at 4 in W.C. (1000 Pa) grams — 371 (cylindrical elementonly) Water Spray Test-final dP in. H₂O — 5.2 Pa 1300 Water SprayTest-water downstream ml — 0

Example 3

Laminated filter media were prepared using the following technique. Aroll of polypropylene melt-blown filter material was purchased from H&Vof (Floyd, Va.) (Product Number PE13030CA, electrostatically charged asobtained from the supplier). A 50 gsm wet-laid filter material thatincludes a mixture of glass and bicomponent fibers was prepared similarto that of Example 6 in U.S. Pat. No. 7,314,497 (with the modificationthat it consists of 50% B08 microglass fibers from Lauscha FiberInternational (Lauscha, Germany) and 50% bicomponent PET fibers (TJ04BN)from Teijin (Osaka, Japan)). A spunbond support material of FINON C310NWwas purchased from Midwest Filtration of Cincinnati, Ohio. The sheetproperties are in Table 5.

TABLE 5 Properties of the components of Example 3 FINON Property UnitsEN0701937 PE13030CA C310NW Basis Weight lbs./3000 ft² 30.5 18.4 61.5grams/m² 50 30 100 Fiber Size μm 0.8/14 2.9 17.4 Thickness (1.5 psi)Inches 0.0115 0.0101 0.008 Mm 0.292 0.257 0.203 Frazier Permeability @0.5 in Fpm 10.10 47.50 108.00 H₂O (125 Pa) 1/m²/sec 81 380 864Hydrostatic Head Mb 16.00 41.50 6.00 NO IPA MPPS DEHS efficiency % 98.8196.69 <10% 4 fpm (2.0 cm/s) Post IPA soak MPPS DEHS % 98.03 40.21 <10%efficiency 4 fpm (2.0 cm/s)

These three rolls were layered so that the melt-blown layer wasupstream, the wet-laid layer was in the middle and the spunbond layerwas downstream. The three layers were heat laminated at 265° F. using acopolyester hotmelt adhesive available under the tradename GRILTEX 9E, agranular adhesive from EMS-Griltech of Switzerland, at a rate of 4.07g/m² between each layer.

The material was then corrugated to an average depth of 0.0302 inch(0.762 mm) (measuring the distance in the z direction from the top ofthe peak to the bottom of the trough on the wire side of the media) with4.5 corrugations per inch (1.77 corrugations/cm). The flat sheet mediawas pleated at 2 inches (5.1 cm) pleat depth (with PLEATLOC Separation)and built into 26-inch (66-cm) conical and cylindrical filter pairs. Theconical elements had 280 pleats per element while the cylindricalelements had 230. The elements were built such that the melt-blown layerwas facing upstream.

The laminated and corrugated media was tested for its flat sheetproperties, and the elements were tested for efficiency, waterrepellency and dust holding capacity using EN1822, the Water Spray Test,and the dust holding capacity test (DHC) as per EN779:2012 respectively.The results are shown in Table 6.

TABLE 6 Properties of the laminated media Example 3 Example 3 beforeafter Property Units corrugation corrugation Basis Weight lbs./3000 ft²110.4 110.4 grams/m² 180 180 Thickness (1.5 psi) inches 0.0313 Mm 0.795Frazier Perm @ 0.5 in H₂O (125 Pa) Fpm 7.95 7.70 1/m²/sec 63.6 61.6Hydrostatic Head Mb 86.33 10.33 NO IPA MPPS DEHS efficiency % 99.9799.46 4 fpm (2 cm/s) Post IPA soak MPPS DEHS % 99.39 95.93 efficiency 4fpm (2 cm/s) Flat sheet salt loading at 10 inches (2500 Mg 142.00 180.00Pa) and 3.6 fpm (1.8 cm/s) for 62 cm² Corrugation Depth Inches — 0.030Mm 0.762

Example 4

Laminated filter media were prepared using the following technique. Aroll of polypropylene melt-blown filter material was purchased from H&Vof Floyd, Va. (Product Number PE13030CA, electrostatically charged asobtained from the supplier). A 50 gsm wet-laid filter material includinga mixture of glass and bicomponent fibers was prepared similar to thatof Example 6 in U.S. Pat. No. 7,314,497 (with the modification that itconsists of 50% B08F microglass fibers from Lauscha Fiber Interational(Lauscha, Germany) and 50% bicomponent PET fibers (TJ04BN) from Teijin(Osaka, Japan)). A spunbond support material of FINON C310NW waspurchased from Midwest Filtration of Cincinnati, Ohio. The sheetproperties are in Table 7.

TABLE 7 Properties of the components of Example 4 FINON Property UnitsEN0701937 PE13030CA C310NW Basis Weight lbs./3000 ft² 30.5 18.4 61.5grams/m² 50 30 100 Fiber Size μm 0.8/14 2.9 17.4 Thickness (1.5 psi)Inches 0.0115 0.0101 0.008 Mm 0.292 0.257 0.203 Frazier Permeability @0.5 in Fpm 10.10 47.50 108.00 H₂O (125 Pa) 1/m²/sec 81 380 864Hydrostatic Head Mb 16.00 41.50 6.00 NO IPA MPPS DEHS efficiency % 98.8196.69 <10% 4 fpm (2 cm/s) Post IPA soak MPPS DEHS % 98.03 40.21 <10%efficiency 4 fpm (2 cm/s)

These three rolls were layered so that the melt-blown layer wasupstream, the spunbond layer was in the middle, and the wet-laid layerwas downstream. The three layers were heat laminated at 265° F. using acopolyester hotmelt adhesive available under the tradename GRILTEX 9E, agranular adhesive from EMS-Griltech of Switzerland, at 4.07 g/m² betweeneach layer.

The material was then corrugated to an average depth of 0.031 inch(0.787 mm) (measuring the distance in the z direction from the top ofthe peak to the bottom of the trough on the wire side of the media) with4.5 corrugations per inch (1.77 corrugations/cm). The flat sheet mediawas pleated at 2 inches (5.1 cm) pleat depth (with PLEATLOC separation)and built into 26-inch (66-cm) conical and cylindrical filter pairs. Theconical elements had 280 pleats per element while the cylindricalelements had 230. The elements were built such that the melt-blown layerwas facing upstream.

The laminated and corrugated media was tested for its flat sheetproperties, and the elements were tested for efficiency, waterrepellency and dust holding capacity using EN1822, the Water Spray Test,and the dust holding capacity test (DHC) respectively. The results areshown in Table 8.

TABLE 8 Properties of the laminated media and element for Example 4Example 4 Example 4 before after Property Units corrugation corrugationBasis Weight lbs./3000 ft² 110.4 110.4 grams/m² 180 180 Thickness (1.5psi) Inches 0.0327 Mm 0.831 Frazier Perm @ 0.5 in H₂O (125 Pa) Fpm 7.657.35 1/m²/sec 61.2 58.8 Hydrostatic Head Mb 77.67 20.17 NO IPA MPPS DEHSefficiency % 99.95 99.89 4 fpm (2 cm/s) Post IPA soak MPPS DEHS % 99.3698.01 efficiency 4 fpm (2 cm/s) Flat sheet salt loading at 10″ (2500 Pa)Mg 182.00 172.00 and 3.6 fpm (1.8 cm/s) for 62 cm² Corrugation DepthInches — 0.031 Mm 0.787 Element dP in. H₂O — 1.00 Pa 250 ElementEfficiency (pre IPA) % — 99.10 Element Efficiency (post IPA) % — 97%Element DHC at 4 in W.C. (1000 Pa) Grams — 1601 (pair) Water SprayTest-final dP in. H₂O — 1.8 Pa 450 Water Spray Test-water downstream Ml— 0

Example 5

Laminated filter media was prepared using the following technique. Aroll of polypropylene melt-blown filter material was purchased from H&Vof Floyd, Va. (Product Number PE13030CA, electrostatically charged asobtained from the supplier). A 50 gsm wet-laid filter material includinga mixture of glass and bicomponent fibers was prepared similar to thatof Example 6 in U.S. Pat. No. 7,314,497 (with the modification that itconsists of 50% B08F microglass fibers from Lauscha Fiber Interational(Lauscha, Germany) and 50% bicomponent PET fibers (TJ04BN) from Teijin(Osaka, Japan)). A spunbond support material of FINON C310NW waspurchased from Midwest Filtration of Cincinnati, Ohio. The sheetproperties are in Table 9.

TABLE 9 Properties of the components of Example 5 PE13030 FINON PropertyUnits EN0701937 CA C310NW Basis Weight lbs./3000 ft² 30.5 18.4 61.5grams/m² 50 30 100 Fiber Size μm 0.8/14 2.9 17.4 Thickness (1.5 psi)Inches 0.0115 0.0101 0.008 Mm 0.292 0.257 0.203 Frazier Permeability @0.5 in Fpm 10.10 47.50 108.00 H₂O (125 pa) 1/m²/sec 81 380 864Hydrostatic Head Mb 16.00 41.50 6.00 NO IPA MPPS DEHS efficiency % 98.8196.69 <10% 4 fpm (2 cm/s) Post IPA soak MPPS DEHS % 98.03 40.21 <10%efficiency 4 fpm (2 cm/s)

These three rolls were layered so that the melt-blown layer wasupstream, the spunbond layer was in the middle and the wet-laid layerwas downstream. The three layers were heat laminated at 265° F. using acopolyester hotmelt adhesive available under the tradename GRILTEX 9E, agranular adhesive from EMS-Griltech of Switzerland, at a rate of 4.07g/m² between each layer.

The material was then corrugated to an average depth of 0.027 inch(0.686 mm) (measuring the distance in the z direction from the top ofthe peak to the bottom of the trough on the wire side of the media) with4.5 corrugations per inch (1.77 corrugations/cm). The flat sheet mediawas pleated at 2 inches (5.1 cm) pleat depth (with PLEATLOC separation)and built into 26-inch (66-cm) conical and cylindrical filter pairs. Theconical elements had 280 pleats per element while the cylindricalelements had 230. The elements were built such that the melt-blown layerwas facing upstream.

The laminated and corrugated media was tested for its flat sheetproperties, and the elements were tested for efficiency, waterrepellency and dust holding capacity using EN1822, the Water Spray Test,and the dust holding capacity test (DHC) respectively. The results areshown in Table 10.

TABLE 10 Properties of the laminated media and element for example 5Example 5 Example 5 before after Property Units corrugation corrugationBasis Weight lbs./3000 ft² 110.4 110.4 grams/m² 180 180 Thickness (1.5psi) Inches 0.0307 Mm 0.780 Frazier Permeability @ 0.5 in Fpm 7.30 7.20H₂O (125 Pa) 1/m²/sec 58.4 57.6 Hydrostatic Head Mb 79.67 76.17 NO IPAMPPS DEHS efficiency % 99.94 99.96 4 fpm (2 cm/s) Post IPA soak MPPSDEHS % 99.40 98.90 efficiency 4 fpm (2 cm/s) Flat sheet salt loading at10″ (2500 Pa) Mg — 217.00 and 3.6 fpm (1.8 cm/s) at 62 cm² CorrugationDepth Inches — 0.027 Mm 0.686 Element dP in. H₂O — 1.10 Pa 275 ElementEfficiency (pre IPA) % — 99.88 Element Efficiency (post IPA) % — 98.27Element DHC at 4 in W.C. (1000 Pa) Grams — 731 (cylindrical only) WaterSpray Test-final dP in. H₂O — 2.35 Pa 588 Water Spray Test-waterdownstream Ml — 2.50

Example 6

Laminated filter media are prepared using the following components: aroll of polypropylene melt-blown fibers, a wet-laid roll including amixture of glass and bicomponent PET fibers, a roll of spunbond verysimilar to the ones cited above. A roll of scrim is used to create alayer downstream from the glass-containing layer. The scrim has a veryhigh perm (greater than 16001/m²/s) and as thin as possible (less than0.005 inch) so there is a minimal effect on the flat sheet or filterelement performance.

The four layers are laminated together so the melt-blown layer is thefurthest upstream, the spunbond is downstream from the melt-blown layer,the wet-laid glass-containing layer is just downstream of the spunbondlayer, and the scrim is on the most downstream side. The adhesive (e.g.,the adhesive used in Examples 1, 3, 4, and 5) used during lamination ischosen to minimize the effect it would have on the laminated structure(i.e., the permeability of the 4 layers together without any glue issimilar to that of the laminate). The material could then be corrugatedand pleated into 26-inch (66-cm) conical and cylindrical pairs.

Example 7

Any of the filter media of Examples 1 through 6 are built with aglass-containing layer that has been hydrophobically treated to improvewater repellency. Data is shown below.

TABLE 11 Properties of the components of Example 7 Treated FINONProperty Units EN0701937 PE13030CA C310NW Basis Weight lbs./3000 ft²30.5 18.4 61.5 grams/m² 50 30 100 Fiber Size μm 0.8/14 2.9 17.4Thickness (1.5 psi) Inches 0.094 0.0101 0.008 Mm 0.24 0.257 0.203Frazier Permeability @ 0.5 in Fpm 8.1 47.50 108.00 H₂O (125 Pa) 1/m²/sec64.8 380 864 Hydrostatic Head Mb 61 41.50 6.00 NO IPA MPPS DEHSefficiency % 98.8 96.69 <10% 4 fpm (2 cm/s) Post IPA soak MPPS DEHS %98.9 40.21 <10% efficiency 4 fpm (2 cm/s)

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this disclosure will become apparent tothose skilled in the art without departing from the scope and spirit ofthis disclosure. It should be understood that this disclosure is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the disclosureintended to be limited only by the claims set forth herein as follows.

1-20. (canceled)
 21. A filter medium comprising: a melt-blown filterlayer comprising melt-blown fibers; a high-efficiency glass-containingfilter layer comprising glass fibers and multi-component binder fibers;and a support layer; wherein at least one of the layers comprises ahydrophobic material.
 22. The filter medium of claim 21, wherein thehydrophobic material comprises a hydrophobic coating.
 23. The filtermedium of claim 22, wherein the hydrophobic coating is on thehigh-efficiency glass-containing filter layer.
 24. The filter medium ofclaim 21, wherein the hydrophobic material comprises a polyolefin. 25.The filter medium of claim 21, wherein the glass fibers have an averagediameter of less than 2 μm.
 26. The filter medium of claim 21, whereinthe glass-containing filter layer is positioned between the melt-blownfilter layer and the support layer, and wherein the melt-blown filterlayer is the upstream-most layer of the filter medium.
 27. The filtermedium of claim 21, wherein the multi-component binder fibers of theglass-containing filter layer comprises bicomponent fibers having a lowmelting point polyester sheath and a higher melting point polyestercore.
 28. The filter medium of claim 21, wherein the melt-blown filterlayer is electrostatically charged.
 29. The filter medium of claim 21,wherein the support layer comprises a spunbond layer.
 30. The filtermedium of claim 21, wherein the filter medium is watertight, as measuredusing the Water Spray Test.
 31. The filter medium of claim 30, whereinthe filter medium displays a hydrostatic head of at least 10 inches(25.4 cm) of water.
 32. The filter medium of claim 21, wherein theglass-containing filter layer has a solidity of 5% to 20%.
 33. Thefilter medium of claim 21, wherein the filter medium exhibits a dustloading capacity of at least 30 grams per square foot (g/ft²) of ASHRAEdust when loaded to 4 inches of water dP in static mode.
 34. The filtermedium of claim 21, wherein the filter medium exhibits an efficiency ofat least E10.
 35. A filter element, wherein the filter element comprisesa media pack comprising a filter medium, wherein the filter mediumcomprises: a melt-blown filter layer comprising melt-blown fibers; ahigh-efficiency glass-containing filter layer comprising glass fibersand multi-component binder fibers; and a support layer; wherein at leastone of the layers comprises a hydrophobic material, wherein themelt-blown filter layer is the most upstream layer and theglass-containing layer is positioned adjacent to the melt-blown layer,and wherein the filter element comprises a cylindrical elementcomprising the media pack.
 36. The filter element of claim 35, whereinthe cylindrical element is axially aligned with a second cylindricalelement or wherein the cylindrical element is axially aligned with apartially conical element.
 37. A method of preparing filter media, themethod comprising: preparing a glass-containing filter layer from amixture of glass fibers and multi-component binder fibers using awet-laid process; laminating the glass-containing filter layer between amelt-blown filter layer comprising melt-blown fibers and a supportlayer.
 38. The method of claim 37 further comprising rendering theglass-containing filter layer hydrophobic by plasma treatment or byapplying a hydrophobic coating.
 39. A method of filtering air, themethod comprising directing the air through a filter medium comprising:a melt-blown filter layer comprising melt-blown fibers; ahigh-efficiency glass-containing filter layer comprising glass fibersand multi-component binder fibers; and a support layer; wherein at leastone of the layers comprises a hydrophobic material.
 40. The method ofclaim 39, further comprising directing air to be filtered into a hoodarrangement, and from the hood arrangement, directing the air into alouver arrangement.